Unable to cast COM object" error

  • Thread starter Thread starter Emrak
  • Start date Start date
E

Emrak

Hey all, I receive the following error:
Unable to cast COM object of type 'System.__ComObject' to interface type
'Microsoft.Office.Interop.Outlook._MailItem'.

I will demonstrate the 3 main attempts (of the trillion I've tried). :-/

Attempt #1:
oOutlook = new Outlook.Application();
oNs = oOutlook.GetNamespace("MAPI");
oFldr = oNs.Folders["Public Folders"].Folders["Test"]

foreach (MailItem oMessage in oFldr.Items)
{
....
}

Attempt #2:
oOutlook = new Outlook.Application();
oNs = oOutlook.GetNamespace("MAPI");
oFldr = oNs.Folders["Public Folders"].Folders["Test"]

foreach (Object oMessage in oFldr.Items)
{
....
}

Attempt #3:
oOutlook = new Outlook.Application();
oNs = oOutlook.GetNamespace("MAPI");
oFldr = oNs.Folders["Public Folders"].Folders["Test"]

for (int i = 1; i <= oFldr.Items.Count; i++)
{
Object o = oFldr.Items;
Type t = o.GetType();
}

I know that people are wont to send in email types other than MailItem. For
instance, there are several "discussion" items in the email box in question.
I've tried to isolate those, but when I run #3, I find that "oFldr.Items"
has a type of "System.__ComObject" which is unhelpful to me. All I'm trying
to do is grab email messages and discussion items and process them.
Unfortunately, it bombs out.

Help!
 
Don't multipost. Also, always post your Outlook version.

You need to do a logon to NameSpace if you are using this code in a
standalone appliation. If it's a COM addin use the application object passed
to you in your connection handler. You also need to refer to the Public
Folders tree correctly.

object _missing = System.Reflection.Missing.Value;

oOutlook = new Outlook.Application();
oNs = oOutlook.GetNamespace("MAPI");
oNs.Logon(_missing, _missing, _missing, _missing);
oFldr =
oNs.GetDefaultFolder(Outlook.OlDefaultFolders.olPublicFoldersAllPublicFolders
).Folders["Test"];

for (int i = 1; i <= oFldr.Items.Count; i++)
{
Object o = oFldr.Items;
object[] args = new Object[] { };
Type t = o.GetType();
object retVal = o.InvokeMember("Class", BindingFlags.Public |
BindingFlags.GetField |
BindingFlags.GetProperty, null, o, args);

Outlook.OlObjectClass itemClass = (Outlook.OlObjectClass)retVal;
if (itemClass == Outlook.OlObjectClass.olNote)
{
// it's a mail item
Outlook.MailItem oMail = (Outlook.MailItem)o;
}
}

There are plenty of Outlook code samples in C# at www.outlookcode.com, my
Web site, the MS Office Developer Web site and many other places. It might
be helpful to you to study some of the code to see how things are done.

What I showed has no error handling, something especially needed in managed
code.




Emrak said:
Hey all, I receive the following error:
Unable to cast COM object of type 'System.__ComObject' to interface type
'Microsoft.Office.Interop.Outlook._MailItem'.

I will demonstrate the 3 main attempts (of the trillion I've tried). :-/

Attempt #1:
oOutlook = new Outlook.Application();
oNs = oOutlook.GetNamespace("MAPI");
oFldr = oNs.Folders["Public Folders"].Folders["Test"]

foreach (MailItem oMessage in oFldr.Items)
{
...
}

Attempt #2:
oOutlook = new Outlook.Application();
oNs = oOutlook.GetNamespace("MAPI");
oFldr = oNs.Folders["Public Folders"].Folders["Test"]

foreach (Object oMessage in oFldr.Items)
{
...
}

Attempt #3:
oOutlook = new Outlook.Application();
oNs = oOutlook.GetNamespace("MAPI");
oFldr = oNs.Folders["Public Folders"].Folders["Test"]

for (int i = 1; i <= oFldr.Items.Count; i++)
{
Object o = oFldr.Items;
Type t = o.GetType();
}

I know that people are wont to send in email types other than MailItem.
For
instance, there are several "discussion" items in the email box in
question.
I've tried to isolate those, but when I run #3, I find that
"oFldr.Items"
has a type of "System.__ComObject" which is unhelpful to me. All I'm
trying
to do is grab email messages and discussion items and process them.
Unfortunately, it bombs out.

Help!
Click to expand...
 
Good day Mr Slovak,

My apologies for the multipost. Desperation isn't just an 11-letter word.

I have most definitely explored many, many of the programmatic solutions
available online.

My Outlook version is 2003, SP3.

I appreciate your code sample. My main problem at this point (what it has
always been, actually) is not so much handling the "MailItem" objects, but
handling the "discussion" objects. How do I reference them, specifically?
Olnote references only MailItems and not discussions. The bulk of email
received is in a "discussion" format.

Thanks much for your assistance.
 
As an addendum to my last post, I've learned that "Post" is the object type
I'm looking for. As such, I'll demonstrate my current solution for posterity.
I'm using the KISS method here. This works, but I can't determine how, in the
context of "string filter" below, how I'm supposed to code "OR" below. For
instance, MessageClass = NOTE OR POST.




//instanciate variables
Microsoft.Office.Interop.Outlook.Application oOutlook;
Microsoft.Office.Interop.Outlook.NameSpace oNs;
Microsoft.Office.Interop.Outlook.MAPIFolder oFldr;
int iAttachCnt = 0;

oOutlook = new Microsoft.Office.Interop.Outlook.Application();
oNs = oOutlook.GetNamespace("MAPI");

//are there any emails to process?
oFldr = oNs.Folders["Public Folders"].Folders["Test"]

if (oFldr.Items.Count > 0)
{

//cycle through each email, filtering out only messages and posts, no
calendars or tasks

string filter = "[MessageClass] = \"IPM.Note\"";

Microsoft.Office.Interop.Outlook.Items oTestItems =
oFldr.Items.Restrict(filter);
....
}
 
I am making the assumption as of now (tell me if I'm wrong), that I can only
process Posts and Notes separately. I thank you for your time.
 
You can filter or restrict on both Note and Post items in the same filter.
Obviously when you retrieve an Object that could be either you further need
to test for either Class or MessageClass to know which type to assign that
Object.

However, unless you don't have any possibility of running into custom forms
or want to exclude all custom forms you are probably best off using a filter
that checks for the MessageClass starting with "IPM.Note" or starting with
"IPM.Post". That's easiest to do using the undocumented capability of using
SQL type statements in a filter.

That filter would look something like this. The DASL property tags aren't
URL's, they are actually the DASL equivalent of "MessageClass".

"http://schemas.microsoft.com/mapi/proptag/0x001a001e" LIKE 'IPM.Note%' OR
"http://schemas.microsoft.com/mapi/proptag/0x001a001e" LIKE 'IPM.Post%'

I'd construct that using StringBuilder myself probably:

StringBuilder sb = new StringBuilder();

sb.Append(@"http://schemas.microsoft.com/mapi/proptag/0x001a001e" + @" LIKE
'IPM.Note%' OR" + @"http://schemas.microsoft.com/mapi/proptag/0x001a001e" +
@" LIKE 'IPM.Post%'");

string filter = "@SQL=" + sb.ToString();

Microsoft.Office.Interop.Outlook.Items oTestItems =
oFldr.Items.Restrict(filter);
 
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